The invention concerns a method for automatically controlling a marine propulsion system with a surface-piercing propeller.
Surface-piercing propellers are often used in fast ships. Surface-piercing propellers can be varied both in their depth of immersion and towards port or starboard to control the ship. Hereinafter, the depth of immersion of the surface-piercing propeller will be referred to as the trim position. In this regard, a trim position of +100% corresponds to a maximum emersion position, and a trim position of −100% corresponds to a maximum immersion depth of the propeller. In practice, a ship's navigator sets the subjectively best trim position by means of a control element. However, this results in an additional burden on the navigator besides his nautical tasks. During dynamic operations, he often lacks the criteria for evaluating the best trim position.
WO 2004/020281 A1 discloses a measure for improving this situation. It proposes a method for automatically adjusting a surface-piercing propeller as a function of the current operating state of the ship. The current operating state in turn is derived from the ship's speed, a steering angle, the position of a throttle control, and parameters of the internal combustion engine. However, this source does not describe a practical embodiment.
DE 195 15 481 A1 discloses a method and a device for the automatic load control of a marine propulsion system with a variable-pitch propeller. This device comprises a closed-loop speed control system for automatically controlling the speed of revolution of the internal combustion engine and a system controller for controlling the variable-pitch propeller. From the power desired by the navigator, i.e., the throttle control setting, a set speed is computed by a first engine map as a reference input for the closed-loop speed control system. A set blade pitch to be used as a setpoint value for the system controller is likewise derived from the power desired by the navigator by means of a second engine map. The set blade pitch is then converted by the system controller to an actuating variable for the variable-pitch propeller. This process also takes into account the power reserve of the internal combustion engine, a speed control deviation, and a speed gradient in accordance with an increase or decrease of the blade pitch.
In this method, a large change in the desired power brings about a change in the set speed and the set blade pitch that is immediate and in the same direction. The closed-loop speed control system has a large system-related step response time. Therefore, a change in the correcting variable, for example, the injection quantity, produces a change in the actual speed and in the quantities derived from it only after a time delay. The set blade pitch, on the other hand, is rapidly converted by the control unit to an actuating variable for the variable-pitch propeller. Since the variable-pitch propeller with the adjustment hydraulics has a large time constant, this response is moderated.
The method known from DE 195 15 481 A1 cannot be exactly translated to a marine propulsion system with a surface-piercing propeller. The reason for this is the significantly shorter response time of the surface-piercing propeller compared to a variable-pitch propeller. For example, an exact translation would cause a large load on the internal combustion engine after a change in the amount of power desired, and as a result, the acceleration of the ship would be delayed.